Just to add one more comment about Server Side Includes.

If you tried the code I posted earlier and it did not include your .html file as expected, it is probably due to your server's configuration.
So if the above code doesn't include your .html files properly, then you'll have to rename your .html files to .shtml.

You would then use the following:
The reason why the .shtml extension is often required is so that the server doesn't waste time and resources searching through every .html file for an include statement. By giving a .shtml extension, the server will only expect an include to possibly occur in that filetype.

Note: You can use either .shtml or .shtm.